1. Field of the Invention
The present invention relates to a pinch roller apparatus used for a tape recorder, a VTR or the like.
2. Description of the Background Art
A pinch roller apparatus includes a rotationally driven capstan, and a pinch roller including a roller body pressed against the capstan. A tape is pinched between the capstan and the roller body which are in pressure contact, and moved in a prescribed direction.
General requirements for the pinch roller include tape running stability and durability of the pinch roller itself.
One factor determining the tape running stability is a self alignment function of the pinch roller. By the self alignment function, error or difference in parallelism between the axis of the capstan and the pinch roller, which is inevitable in design and manufacturing, is absorbed by a play in the direction of inclination of the roller body of the pinch roller with respect to the roller shaft, so that the axis of rotation of the roller body is made parallel to the axis of rotation of the capstan. When the pinch roller does not have a self alignment function or the pinch roller has a poor self alignment function, the following phenomenon occurs, degrading tape running stability. For example, tape pinching pressure may be biased, resulting in irregular stretching of the tape. The tape may possibly fall off from the pinch roller. Further, the tape may deviate upward or downward, or the speed of running of the tape may fluctuate, resulting in increased wow and flutter.
In a typical structure of a conventional pinch roller, a roller body having an elastic body such as rubber fixed on an outer peripheral surface of a cylindrical sleeve is rotatably attached on a roller shaft by means of a ball bearing. In such a structure, a very precise and small ball bearing is necessary, and hence manufacturing cost of the pinch roller is high.
In view of the foregoing, application of a plain bearing formed of resin or sintered metal which has a simple structure and is inexpensive to the pinch roller instead of the ball bearing has been proposed. FIG. 8 is an illustration showing a self alignment function of the pinch roller employing the plain bearing. When roller shaft 1 is inclined with respect to a capstan 6, roller body 3 is inclined with respect to roller shaft 1 because of a clearance provided between bearing 2 and roller shaft 1. As a result, the axis of rotation of the roller body 3 becomes parallel to the axis of the capstan 6. In the figure, reference numeral 7 represents a tape, 4 represents a metal sleeve and 5 represents a cylindrical elastic body.
However, when a large clearance is provided between bearing 2 and roller shaft 1, only the upper or lower end of the bearing 2 will be brought into contact with the roller shaft, resulting in local sliding, which causes severe friction at the upper and lower ends of the bearing 2, promoting local wear. Therefore, it becomes difficult to satisfy the requirement of durability of the pinch roller.
In a structure such as shown in FIG. 8, it is possible that the roller body 3 is largely inclined not only with respect to the direction of the capstan 6 but also to the direction of running of tape 7 orthogonal thereto. When the roller body 3 is inclined significantly in the direction of tape running by some cause such as vibration or shock at the time of mode switching, the roller body 3 and the capstan 6 will be in point contact and not in line contact. In this case, pressure does not act uniformly in the widthwise direction of the tape 7 pinched therebetween, causing irregular stretch of the tape 7. In addition, wow and flutter are increased because of snaking or upward/downward movement of the tape 7, so that it is difficult to satisfy the tape running stability.